The subject of this invention is an internal stator shroud.
Controlling thermal expansion has become essential in the field of turbojet engines in order to ensure high efficiency through regulation of the clearance between the stator and the moveable rotor blade ends. A frequently encountered stator structure is a dual one and includes a housing surrounding an internal shroud in contact with the propulsion gases of the machine. It is common in such a case for the external housing to be formed all in one piece so that it has good mechanical resistance and may be cooled by ventilation with a high level of consistency helped by its continuity, but for the shroud on the other hand to be composite, formed of successive component circumferences in a circle sector. By means of this arrangement, the internal stresses, which might have developed in the shroud from its being joined to the more rigid housing and from exposure to the hot gases in the vein, remain at a moderate level, and the different circumferences may be ventilated at different intensities in order to regulate their diameters independently. The prior art includes a certain number of examples of this dual stator, among which may be cited French patents 2 683 851 and 2 695 164 issued to the applicant.
FIG. 1 shows one of these designs, wherein the external housing is denoted 1, the shroud components are denoted 2 and the rotor is denoted 3; the shroud components 2 are joined to the adjacent components 2, located on the adjoining circumferences, by joints 4 composed of a tenon 5 on one of the components 2 and a groove 6, into which the tenon 5 penetrates, on the other of the components 2. Fixing points 7, better shown in FIG. 2, connect the shroud components 2 to the housing 1. They include essentially a bolt 8 engaged through a boss 9 of the housing 1 and a housing 1 contact bearing 10, located at the end of a rib 11 of the shroud component 2. The bolts 8 are in general placed obliquely in order to provide the axial and radial holding of the rectifier sectors (the shroud components 2). Circular resilient joints 12 are placed at the back of the circumferences of the shroud components 2 and include a heel 13 held tightly between the contact bearing 10 and a shoulder 14 of the housing 1 and, rising under the heel 13, a sealing lip 15 the end of which is supported on a plane sealing face 16 at the back of the shroud components 2. In this way, individual chambers 17 are isolated between the housing 1 and each of the shroud component circumferences 2.
The objective of obtaining good regulation of the diameters of the shroud circumferences is however not fully met, since variations in diameter and rippling of the circumferences can easily occur.
This drawback is attributed here to the presence of the fixing points 7, which seem like structural irregularities in the shroud components 2. More exactly, the inventors have considered that the presence of a plurality of fixing points 7 was harmful and propose using only one of them per shroud component 2.
Since a single fixing point would not by itself allow a shroud component to be held in a satisfactory way, it is further advocated to use a single support point per shroud component 2 in place of the eliminated fixing points. This support point includes a tenon fixed to the shroud component and penetrating into a groove of an associated flange, which is fixed to the housing. The shroud components have the ability to be displaced slightly in the axial and circumferential directions of the machine at the support point by a sliding of the tenons in the grooves, without excessive displacements being tolerated since stop states would be reached. In this way is achieved a suitable joint of the shroud components to the housing and a flexibility of assembly which prevents them being distorted unevenly.